June 16, 2010 at 8:54 am
I've set up a disk space monitoring service and found many drives with under 10% free space available. Many of these are the OS drives though and aren't expected to grow much.
Are there any heuristics or standards on how much space should be left free on a volume? Are there technical reasons for these numbers? I've been looking around for any kind of article or white paper but haven't had much luck.
I know lots of monitoring systems will send alerts at less than 20% free.
June 16, 2010 at 8:57 am
20% is a standard threshold because NTFS starts degrading performance under 15% of free space.
I would recommend that percentage: it lets you discover problems before they arise.
-- Gianluca Sartori
June 16, 2010 at 9:04 am
It all depends on the type of storage subsystem as well as on how the target database uses allocated space e.g. select/insert/update/delete.
On the other hand let me point to two issues.
1- Physical drives don't like to be full.
2- Disk performance on external tracks usually is twice as good as disk performance on inner tracks so - as a rule of thumbs - the more free space you have in the drive the less used are inner tracks therefore the more juice you get from your storage subsystem.
_____________________________________
Pablo (Paul) Berzukov
Author of Understanding Database Administration available at Amazon and other bookstores.
Disclaimer: Advice is provided to the best of my knowledge but no implicit or explicit warranties are provided. Since the advisor explicitly encourages testing any and all suggestions on a test non-production environment advisor should not held liable or responsible for any actions taken based on the given advice.June 16, 2010 at 11:06 am
Good feedback, thanks.
I think my biggest battle would be convincing others here to expand C drive volumes. These are going to be local physical arrays of RAID 1 and likely are using SAS drives.
Your statements seem to match other stuff I've come across.
I've kept doing some more hunting for anything that I can use to show management here.
It is recommended that you maintain about 30 percent of any NTFS-formatted disk as free space to ensure that you have sufficient room for effective defragmentation.
@ http://technet.microsoft.com/en-us/library/bb742585.aspx
The less data a disk has on it, the faster it will operate. This is because on a well defragmented drive, data is written as close to the outer edge of the disk as possible, as this is where the disk spins the fastest and yields the best performance.
Disk seek time is normally considerably longer than read or write activities. As noted above, data is initially written to the outside edge of a disk. As demand for disk storage increases and free space reduces, data is written closer to the center of the disk. Disk seek time is increased in locating the data as the head moves away from the edge, and when found, it takes longer to read, hindering disk I/O performance.
This means that monitoring disk space utilization is important not just for capacity reasons but for performance also.
As a rule of thumb, work towards a goal of keeping disk free space between 20% to 25% of total disk space. If free disk space drops below this threshold, then disk I/O performance will be negatively impacted.
@ http://msdn.microsoft.com/en-us/library/ee377075(BTS.10).aspx
June 16, 2010 at 11:16 am
Robert Biddle (6/16/2010)Your statements seem to match other stuff I've come across.
... are we good or what? 😀 Glad to help.
_____________________________________
Pablo (Paul) Berzukov
Author of Understanding Database Administration available at Amazon and other bookstores.
Disclaimer: Advice is provided to the best of my knowledge but no implicit or explicit warranties are provided. Since the advisor explicitly encourages testing any and all suggestions on a test non-production environment advisor should not held liable or responsible for any actions taken based on the given advice.Viewing 5 posts - 1 through 4 (of 4 total)
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